The present invention relates to a computer system, and more particularly to a computer system provided with a storage device subsystem having both an interface compatible to a count-key data format and an interface compatible to a fixed length block format.
So-called down sizing which conducts applications which have heretofore been conducted in a main frame by using a so-called open system such as a personal computer or a workstation has recently been becoming popular. A large volume of information is stored in the main frame by the applications conducted heretofore and there is a big demand to access the information stored in the main frame from the open system. In the past, as for the sharing or file transformation of files between different operating systems, a technique to access a file in the MS-DOS operating system which is a personal computer operating system of the Microsoft Inc., USA, from the UNIX operating system on a workstation (operating system licensed by the X/Open Company Ltd., has been known.
Generally, in a computer system, information is stored in a storage device such as a disk storage. The main frame traditionally desired to use the disk access in the count-key-data format while the open system desires to use the disk access in the fixed length block format. Thus, the information used on the disk used in the main frame cannot be directly used from the open system. As techniques to access the information on the disk used in the main frame from the open system, a distributed database and a technique to utilize a file transfer have been known but such techniques have drawbacks in that they impose a heavy workload to a network and need modification of existing application programs.
It is an object of the present invention to allow the direct access to information stored in a disk storage by a computer which conduct the disk access in accordance with a count-key-data format from a computer provided with an interface which conducts the disk access in accordance with a fixed length block format.
A computer system in accordance with the present invention comprises a first computer (main frame) which conducts the disk access in accordance with the count-key-data format, a second computer (open system) which conducts the disk access in accordance with the fixed length block format and a disk subsystem connected to the first and second computers. The disk subsystem comprises a first interface which is connected to the first computer and compatible to the count-key-data format, a second interface which is connected to the second computer and compatible to the fixed length data format and means for reading the information from the disk storage in accordance with a fixed length data format address received from the second interface and transferring the read information to the second computer in a fixed length data format block unit through the second interface. The second computer comprises means for accepting a disk access request compatible to the count-key-data format issued from an application program and converting the count-key-data format address to a fixed length data format address, means for accessing the disk subsystem by using the converted fixed length data format address and means for extracting information designated by the access request from the block-by-block information transferred from the disk subsystem.